Materials such as germanium (Ge), antimony (Sb), and tellurium (Te) can be deposited onto substrates to form GeSbTe (GST) alloys as phase change memory (PCM) materials for use in semiconductor wafers or other semiconductor device structures. The conformal deposition of such materials in the forms of GST films is desirable for use in semiconductor device structures having high aspect ratio topographical features such as vias.
The deposition of GST materials to form films for PCM applications can be carried out using vapor deposition processes, such as chemical vapor deposition (CVD), metalorganic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), or other vapor phase techniques.
PCM technology has the potential to expand commercially into dynamic random access memory (DRAM) and storage class memory (SCM) applications. These applications require long cycling endurance and fast write speeds while maintaining sufficient data retention character, as well as maintaining a low set resistance at small device scales and high aspect ratios. In this respect, alloy compositions and device structure have major and related impact on the PCM performance of the product device. The ability to conformally deposit GST films enables improved PCM cell heating efficiency with lower reset current, by minimizing the amount of GST film material in the cell and reducing heat loss.
Significant efforts are ongoing to improve performance of PCM alloy compositions and device performance (e.g., low reset current, device speed, cycle endurance), relative to that achieved by the GST225 alloy (atomic composition 22.5% Ge, 22.5% Sb, and 55% Te) currently used as a benchmark standard for PCM films and devices.
The processing and handling of Ge, Sb, and Te materials for applying GST films using CVD normally occurs at substrate temperatures above about 300 degrees C. The reason for this is that typical precursors for CVD processes generally utilize such high temperatures to promote molecular reactivity. However, amorphous or partially amorphous GST films are desired to attain the conformal deposition of the films and thus the substrate process temperature is preferred to be below the GST crystallization temperature, which is generally less than about 300 degrees C. This, however, has proven difficult, since tellurium precursors used in chemical vapor deposition processes are difficult to activate and only have suitable reactivity at temperatures typically higher than 300 degrees C. Further, because conventional CVD techniques utilize precursors in the deposition of the GST at processing temperatures of 300 degrees C. and above, the deposition of the GST film generally results in the crystallization of the film and thus is typically not conformal, particularly when Te is present in amounts above about 45% in the product GST film.
There is therefore a compelling need for improved GST films and phase change microelectronic devices utilizing same, e.g., for PCRAM applications.